The yolk of bird eggs contains maternal carotenoids that may act as antioxidants thus influencing offspring performance and survival. However, to our knowledge, this hypothesis has not been subjected to experimental tests and the function of transmission of carotenoids to the egg is largely unknown. We directly manipulated the concentration of the main carotenoid (lutein) in the eggs of barn swallows (Hirundo rustica) and analysed the effect of experimental manipulation on growth of nestlings and two fundamental components of their acquired immunity. Nestlings hatched from lutein-inoculated eggs had larger T-cellmediated immune response compared with those of two control groups. T-cell-mediated immune response predicted nestling survival until fledging. However, lutein inoculation did not affect antibody response to an immunogen, body mass, tarsus length or plumage development. Nestling body mass and plumage development declined with egg laying order, but the effects of lutein inoculation were independent of egg laying order for all traits. Our results show that maternal yolk carotenoids can have a major effect in promoting a fundamental component of immunity that predicts offspring survival and suggests that adaptive early maternal effects can be mediated by transmission of antioxidants to eggs.

Organisms frequently encounter stressful ecological conditions. In vertebrates, a major mechanism of physiological response to stress is mediated by the hypothalamic-pituitary-adrenal axis and results in increased secretion of glucocorticosteroids, which can have adverse consequences on diverse phenotypic traits affecting fitness. Maternal stress may thus have carry-over effects on progeny if it influences pre-natal offspring environment in terms of glucocorticosteroid concentration, although this hypothesis has never been tested in any species under field conditions. We manipulated stress experienced by female barn swallows Hirundo rustica, by exposing them to a predator during laying and measured egg corticosterone concentration. Stressed females laid eggs with greater corticosterone concentration than controls exposed to a herbivore. In another experiment, we injected physiological doses of corticosterone in the egg albumen and compared the phenotype of offspring originating from these eggs with their control siblings originating from either sham-inoculated or unmanipulated eggs and reared in the same nest. Eggs injected with corticosterone had lower hatchability and produced fledglings with smaller body size and slower plumage development than did control eggs. Nestling body size in our study population predicts long-term survival. Thus, maternal stress impaired offspring phenotype and viability by increasing transmission of glucocorticosteroids to the eggs. This study identifies a novel mechanism mediating early maternal effects whereby maternal stress affects offspring quality. These results are relevant to biological conservation because they disclose a mechanism that can link environmental conditions to population productivity and viability.

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Carotenoids are critical to embryonic development, immunity and protection from oxidative stress. Transmission of carotenoids to the eggs may affect development and maturation of immunity in offspring, but carotenoids may be available to females in limiting amounts. Females may thus transfer carotenoids to the eggs differentially in relation to the reproductive value of the offspring as affected by sexual ornamentation of their father. In this study of maternal allocation of carotenoids to the eggs in the barn swallow (Hirundo rustica), females whose immune system had been experimentally challenged with an antigen had smaller lutein concentrations in their eggs than controls. We manipulated the size of a secondary sexual character (tail length) of males, and analysed the effect of manipulation on allocation of lutein to eggs by their vaccinated mates. Contrary to our prediction based on parental allocation theory, mates of tail-shortened males had a larger lutein concentration in their eggs compared with those of control and tail-elongated males. According to previous studies, offspring of short-tailed males have larger exposure and/or susceptibility to parasites. A larger lutein concentration in the eggs of females mated to males with experimentally reduced ornaments may thus reflect adaptive maternal strategies to enhance offspring viability.

Findings indicated that in dogs with cutaneous MCTs, prognostication should not rely on histologic grade alone, regardless of grading system used, but should take into account results of clinical staging.